Hi Marc,
I did a test on my side and can receive the notifications from calendar-nitification@google.com. Moreover, I can trace the messages history using Message Trace in Office 365 side.
So I suggest you contact your admin (if you are not) to perform the message trace to see if the messages are blocked. Please make sure your admin role has got Organization Management, Compliance Management, and Help Desk permissions in Exchange admin center-> permissions-> admin roles.
Before running the trace, please try to resend the meeting request to Gmail again and then filtered by your email address. If the notification message can be traced out, you can view the detailed delivery status including the block reason. If no notification message can be traced out, the probable cause is the Gmail doesn’t send any notification out.
To protect your privacy, I have sent you a private message. You can provide the screenshots the trace result with the delivery details by replying to it. To access the private message, please:
1. Go to the Your details section on the right side of the community site.
2. Click Private Messages.
3. Click the subject title of the response to read the message.
To upload the screenshots, you can click Use rich formatting when replying and then click the Insert image button.
Thanks,
Alex